Sometimes It’s OK to Be Stressed: Beneficial H2O and N Stress to Gain Top Yields.

By Bob Gunzenhauser, Director of Agronomy

Neither plants nor animals like to be stressed; we don’t like it when we are rushed to complete a task, a steer isn’t eating as well when it’s 10 F degrees and blowing, and your corn is also not at its best when the leaves are rolling due to drought conditions. 

However, there are times when a little stress may be a good thing; deadlines may be stressful, but they motivate you to get the work done.  In crops, having a little stress at the right time can make a large impact. 

Stress from nitrogen and water are often linked together; water is needed to keep the plants hydrated and osmosis functional, and it is the main delivery method for nitrogen to the plants’ roots.  Without soil water uptake, nitrogen is not easily taken up, either. 

But sometimes stress, applied at the proper time during the development of the plant, can be beneficial.  This can occur by the whims of the weather, or by delaying irrigation. 

During corn’s early to mid-vegetative stages, or approximately V2 to V12, mild water stress can help to conserve water and cause the plant to set deeper roots as it searches for water. Deeper roots will also likely intercept nutrients, including nitrogen, that may not have been accessed by previous growing seasons.  Maintaining the soil moisture during this time at approximately 50-75% of available water capacity (AWC) is key during this time. 

Likewise, holding off larger nitrogen applications until approximately V5-V7 can also cause corn to seek free nitrogen lower in the soil profile through extended rooting.  This can allow for greater nitrogen use efficiency when additional nitrogen is applied shortly after to continue the development of the corn plant. 

An added benefit of maintaining 50-75% AWC during early to mid-vegetative stages is the enhanced opportunity for soil organic matter mineralization, especially at lower depths.  As OM mineralizes, ammonium nitrogen is generated, often quickly converted to nitrate by bacteria.  With the soil moisture being less than field capacity, nitrate-nitrogen will not move quickly nor likely be lost through denitrification.

It is imperative that any kind of controlled stress, either water or nitrogen, is not carried too far.  The “no-go” growth stages for water stress are generally R1 to R3 during key kernel development periods.  For nitrogen, it needs to be available to the corn beginning in the mid-vegetative stages (V6+) to properly build out the solar collection system of leaves to later fill out grain.  If these stress periods are drawn out too long, irreparable damage will occur; immediately addressing the issue through an irrigation or nitrogen application may reduce the impact, but often the damage will have been done. 

An example of beneficial water stress occurred in south-central Iowa on my farm between the fall of 2022 and the growing season of 2023.  Over the winter very little snowfall occurred, and by early April farmers were planting corn at some of the earliest periods they ever had.  Some rain occurred in April and May, but by June it was apparent that the area was experiencing a drought of sorts – some corn, still in mid-vegetative stages, was starting to roll leaves during the heat of the day. 

However, starting in late June and continuing through harvest, periodic showers kept the corn growing, not showing stress during pollination or grain fill.  At harvest, many farmers were surprised by the great yields they had under seemingly drought-like conditions.  Overall, total precipitation was 15-20% less than typical, but yields were much above average. 

This natural stress allowed roots to go deeper during the vegetative stage, unlocking water and nutrients in the typically saturated claypan subsoil.  Because of this, corn became more resilient to additional stress.  Nitrogen was not a limiting factor as it was being supplied by the natural mineralization of the subsoil, aerated by cracks in the upper layers. 

Under irrigated conditions, farmers can induce this sort of scenario by monitoring soil moisture and applying water only to maintain the target soil moisture that enhances rooting development.  Likewise, they can also efficiently meter nitrogen applications that do not overdose the corn but instead provide enough to keep it growing while seeking more in the soil. 

Timely stress, both water and nitrogen, can benefit corn production.  Knowing that roots can seek water and nutrients at deeper levels when they are not available closer to the surface can improve yields and make the corn more resilient to stress later.